Water softeners find wide applications throughout society. In many applications, it is desirable to soften the water by removing the hardness materials, such as calcium and magnesium, from the water before use. This is particularly critical in boiler operations when use of hard water will create boiler scale and rapidly reduce operating efficiencies.
A common water softening process is to use a stand alone water softening tank designed for this purpose. A water softening tank contains cation exchange resin capable of exchanging hardness ions, i.e, calcium and magnesium, for sodium ions which are very soluble. Water to be treated flows in one end of the tank, is treated as it passes through the exchange resin to remove the hardness materials, and flows out of the tank as soft water.
After a certain period of use, the hardness exchanging capacity of the water softening resin becomes exhausted, and it stops producing soft water. It then becomes necessary to regenerate the resin with a saturated solution of sodium or potassium chloride. Because of costs, sodium chloride is usually the chemical of choice. The saturated solution is passed through the resin and the calcium and magnesium ions are replaced by sodium ions to regenerate the resin. The saturated solution now containing the hardness materials is treated as waste water.
Sodium chloride brine solution is created in a separate tank built and designed for this purpose and this tank is called a brine tank. Modern water softeners are well engineered and designed to produce soft water with all regeneration actions done automatically, including the transfer of the saturated brine from the brine tank to the water softening tank.
In order for the water softener resin to be properly rejuvenated, the saturated brine solution must be of a high quality, and a measured volume must be delivered whenever needed. A properly designed and engineered brine tank will provide these needs by delivering a measured quantity of saturated salt brine containing a fixed amount of dissolved salt per gallon of water. This is accomplished by using a horizontal salt grid in a vertical tank positioned at a predetermined height in the tank. Granular salt is supported on this salt grid and the salt fills most of the volume of the brine tank above the grid. The height and diameter of the salt grid varies for each softening system, depending on many factors, but in all cases the height of the grid sets the volume of water in the brine tank. In actual practice, the brine system is set to fill the brine tank with fresh water from the bottom of the tank to approximately one inch above the salt grid and then shut off. Using this method, only one inch of water touches the vertically extending salt pile, which may be several hundred pounds in weight, supported on top of the salt grid.
This system is called a dry salt shelf system, as opposed to a wet salt brine tank system where most or all of the salt is immersed in water. The dry salt shelf system has significant advantages over the wet salt system. The dry salt shelf method produces 100% saturated brine (specific gravity 1.2) all the time where wet salt methods do not. The dry salt shelf system affects more dry salt storage in the same size brine tank than a wet salt system. A dry salt shelf system is easier to keep clean than the wet salt system. A dry salt shelf system does not require a gravel support bed on the bottom of the brine tank. The dry salt shelf system offers lower maintenance costs to the operator, no gravel cleaning or replacement.
The dry salt shelf system uses a brine float or refill valve in the lower section of the brine tank (below the salt grid). The brine refill valve is connected to a riser (a pipe) which extends upwardly to near the top of the brine tank and opens outside the brine tank. Water is both supplied to the brine tank, and removed from the brine tank, through this riser when the refill valve is open. For example, when the brine tank requires filling, fresh water is provided through the riser to the valve to fill the brine tank to a level slightly above the salt grid. A float, operably connected with the brine refill valve, will cause the valve to close when the predetermined quantity of water has been supplied to the tank. After becoming saturated, the water, now a brine solution, is removed through the same riser, past the valve, by drawing a suction in the riser and delivered to the water softening tank to regenerate the resin.
The valve, float and riser are normally positioned within a well (usually a vertical PVC tube), sometimes called a control center, within the brine tank to help isolate these elements from the salt within the tank. The well is typically a vertical PVC pipe, extending from a point 6 to 8 inches below the top of the tank down into the tank to a level somewhat below the salt grid. The top of the well may have a cap to keep salt out of the well interior which might interfere with valve operation. The riser passes through the wall of the well and wall of the tank below the top of the well for external connection.
While this system has worked well, servicing of the valve, float and riser within the well is a complicated procedure. A typical brine tank may be 60 inches tall and 50 inches in diameter. If the brine tank is completely full of salt, salt may in fact cover over the cap on the top of the well near the top of the tank, requiring service personnel to dig down through the salt to reach the cap and remove it to access the well. Service personnel will be required to reach from the top of the brine tank to near the bottom of the tank to service the brine refill valve and float. The salt grid, where the float will be commonly located, may only be 12 inches off the bottom of the tank. The valve itself may rest on the bottom of the tank. A need exists for an improved design providing greater efficiency and more ready accessibility to these components for servicing and repair.